As shown, for example, in FIG. 12, an acoustic diaphragm in a conventional loudspeaker device has a domed diaphragm 121 shaped like a dome in the center, and an edge-like diaphragm 129 which is integrally formed with the domed diaphragm 121 and extending from the circular periphery of the domed diaphragm 121 using a polymer film, metal or the like, such that the edge-like diaphragm 129 has a predetermined curvature of concavity or convexity or is linear in cross section.
A voice bobbin 122 on which a voice coil 123 is wound is joined to a junctional portion where the domed diaphragm 121 and edge-like diaphragm 129 of an acoustic diaphragm 120 are integrated such that the voice bobbin 122 hangs down, and the voice coil 123 is provided to be capable of oscillating up and down as a driving means in a gap 127 which forms a magnetic space.
A frame that constitutes a loudspeaker includes a ring-shaped magnet 124 provided on a disk-like lower surface plate 135 made of metal, a columnar pole piece 125 erected approximately in the center of the lower surface plate 135, a ring-shaped upper surface plate 126 made of metal mounted on the magnet 124, and a cylindrical frame 130 with which the outer circumferential edge of the edge-like diaphragm 129 is fixed; and the voice coil 123 is disposed in the gap 127 formed between the inner circumference of the upper surface plate 126 and the outer circumference of the pole piece 125 to constitute an dynamic loudspeaker device.
When an acoustic signal has been input into a signal input line 128 of a loudspeaker device having such structure, the voice coil 123, which is provided in a magnetic field of the gap 127, generates driving force for oscillating up and down in the gap 127, and emits the acoustic signal by vibrating the acoustic diaphragm 120.
Regarding such a dynamic loudspeaker device as described above, a conventional method of joining the bobbin 122 and the acoustic diaphragm 120 is, for example, shown in FIG. 13. FIG. 13 shows an enlarged view of the part A in FIG. 12, and one end of the cylindrical bobbin 122 on the opposite side to the side where the voice coil 123 is wound is stuck to a domed diaphragm inner circumferential edge portion 133 of the domed diaphragm 121 of the acoustic diaphragm 120 with an adhesive 131.
The acoustic diaphragm 120 is provided continuously to a diaphragm periphery 134, having a curved cross section of convexity or linear cross section, of the edge-like diaphragm 129, through a junctional flat portion 132, which forms a junctional portion vertically bent from the lower end of the domed diaphragm inner circumferential edge portion 133 that is bent downward from the periphery of the domed diaphragm 121, and the diaphragm periphery 134 is fixed to the cylindrical frame 130.
On the other hand, regarding dynamic electromagnetic induction loudspeakers, one having a structure in which a conductive 1-turn ring is wound instead of the voice coil 123 wound on the bobbin 122, and one having a structure in which an upper end of a cylindrical conductive 1-turn ring of a uniform diameter is directly stuck to the domed diaphragm inner circumferential edge portion 133 of the acoustic diaphragm 120 with the adhesive 131 are being proposed.
According to the above-mentioned dynamic loudspeakers or dynamic electromagnetic induction loudspeakers which are compact and capable of reproduction up to high range (for example, to 100 kHz), the acoustic diaphragm 120 including the domed diaphragm 121 and the edge-like diaphragm 129 is obtained by being integrally formed with a thin metal sheet of, such as aluminum, titanium, or with a polymer sheet; consequently, the metal sheet or polymer sheet of the junctional flat portion 132 joining the domed diaphragm 121 and the edge-like diaphragm 129 becomes thin, because the sheet is stretched in both the directions of the domed diaphragm 121 and of the edge-like diaphragm 129, which are opposite to each other, when being formed, hence there is an inconvenience in which mechanical strength lowers.
In addition, if the bobbin 122 shown in FIG. 13 or the conductive 1-turn ring is stuck to the domed diaphragm inner circumferential edge portion 133 and an acoustic signal is input, at a predetermined frequency the domed diaphragm 121 and the edge-like diaphragm 129 generate vibrations respectively whose phase are different by 180 degrees with each other, with the thin, mechanically weak junctional flat portion 132 as a node. On this frequency there has been an inconvenience in which an acoustic signal emitted from the domed diaphragm 121 and an acoustic signal emitted from the edge-like diaphragm 129 cancel out with each other, causing a dip in acoustic pressure. Particularly, if the dip is in the audible band, there is an inconvenience in which the quality of acoustic signals deteriorates.
Further, at a high frequency of 20 kHz or more, driving force from the bobbin 122 or from the conductive 1-turn ring is absorbed by the adhesive 131 and the mechanically weak junctional flat portion 132, so that the driving force is not transmitted to the edge-like diaphragm 129. Thus, a problem in which the necessary acoustic pressure cannot be obtained at a high frequency of 20 kHz or more remains to be solved.
In order to solve the above problems, the inventors of the present invention previously proposed in Japanese Published Patent Application No. 2001-346291 a loudspeaker device in which the mechanical strength of the junctional flat portion 132 is increased by applying the adhesive 131 across the overall width of the junctional flat portion 132 of the acoustic diaphragm 120, and fixing the bobbin 122 to the junctional flat portion 132, as shown in FIG. 14.
Moreover, also a case in which a conductive 1-turn ring 141 shown in FIG. 15 is used as a driving means is disclosed in the above-mentioned gazette. In order for the conductive 1-turn ring 141 to diminish electric resistance thereof, the width t of the end surface thereof is made larger than that of the bobbin 122. In this case, when the width t′ of the junctional flat portion 132, which joins the domed diaphragm 121 and the edge-like diaphragm 129, is approximately equal to the width t of the end surface of the conductive 1-turn ring 141, the mechanical strength of this part further increases.
As described in detail in the above FIG. 14, if the width t of the end surface of the bobbin 122 is smaller than the width t′ of the junctional flat portion 132, reinforcement is required with the adhesive 131; however, in this case, the strength varies depending on the application condition of the adhesive 131.
In addition, to enlarge the width t′ of the junctional flat portion 132 to a great extent causes a problem in terms of design. For example, if the width t of the conductive 1-turn ring 141 is intended to fit the width t′ of the junctional flat portion 132, the magnetic space, namely the width of the gap 127 needs to be enlarged as well, causing an inconvenience in which acoustic pressure sensitivity is lessened.
The present invention is to resolve the above-mentioned problems, and provides a loudspeaker device in which a reinforcement ring is joined to a junctional flat portion or in the vicinity of the junctional flat portion of an acoustic diaphragm to increase the strength of the junctional flat portion, so that vibrations of a domed diaphragm and an edge-like diaphragm that are different in phase by 180 degrees with each other are removed, and driving force from a driving means such as a voice coil is transmitted to the acoustic diaphragm to obtain the excellent quality of acoustic signals up to high range.